Broken-down cart due to malign (7)
I believe the answer is:
traduce
'to malign' is the definition.
('traduce' can be a synonym of 'malign')
'broken-down cart due' is the wordplay.
'broken down' is an anagram indicator.
'cart'+'due'='cartdue'
'cartdue' is an anagram of 'TRADUCE'.
(Other definitions for traduce that I've seen before include "abuse" , "Tell lies about (someone)" , "'Malign, badmouth (7)'" , "Defame, slander" , "Misrepresent in unfavourable way" .)